Why a weekly 50% WC is better than two weekly 25% WCs

[jlnguyen74]

Actually you can.....lol.

You're the second person who told me that.. Look like you two like to play with turd

 

[jcardona1]

It's living with nitrate for longer period is harmful to fish.

In that case, look at vfc's charts. The 50% weekly has nitrate levels from 20-40ppm, while the tank that receives biweekly water changes has nitrate levels from 25-32ppm, all else being equal. Ignore the numbers for a minute, since all tanks are different, but pay attention to the pattern. Wouldn't biweekly be better since you maintain an overall lower nitrate level?

 

[ScatMan]

Many hobbyists perform a 25% water change per week, a 50% water change per week, or some do multiple water changes per week (25% water change two times per week in this example).

One of the primary reasons for performing water changes is to maintain a low nitrate level. When considering nitrate levels, it is obvious why a weekly 50% water change is better than a weekly 25% water change, but it isn't immediately intuitive as to why a weekly 50% water change is better than two 25% water changes per week.

A weekly 50% water change is superior for two main reasons:
1. Nitrate levels reach equilibrium faster (this is minor)
2. Our fish are exposed to a lower average nitrate level each week.

Compare the following data:
(Edit: I apologize but the tables I tried to paste did not format correctly, so just the results are posted. If anyone is interested I can try to post up the data tables)

Scenario 1: Starting at 20ppm nitrate, the nitrate increases 20ppm per week (or 10ppm every 3.5 days). A 25% water change is performed twice per week (every 3.5 days).

Equilibrium is reached where after each 25% water change the nitrate drops to 30ppm, and after 3.5 days it increases to 40ppm.
So at equilibrium:

• Minimum nitrate = 30ppm
• Maximum nitrate = 40ppm
• Average nitrate = 35ppm

Scenario 2: Starting at 20ppm nitrate, the nitrate increases 20ppm per week. A 50% water change is performed each week.In this case, equilibrium is reached immediately, where nitrate is 20ppm after each 50% water change and increases to 40ppm at the end of each week.
So at equilibrium:

• Minimum nitrate = 20ppm
• Maximum nitrate = 40ppm
• Average nitrate = 30ppm

The same amount of water is changed each week, and the maximum nitrate each week is the same for both, but the minimum nitrate is always lower with a 50%wc (in any scenario) resulting in a lower average nitrate per week.
I know this is a lot for what may seem trivial or not very important for many, but I know some, like myself, appreciate data/numbers/evidence for what we do and why we do it. Chronically elevated nitrate levels are now starting to be implicated in some fish diseases, and we are just now starting to have some decent research on nitrate and its role in aquarium health.
For anyone interested, I may be posting some data on recent nitrate research coming from Dr. Floyd at the University of Florida and info from Dr. Weber at the UC Davis School of Veterinary Medicine.

1 large water change keeps your concentrations at a lower minimum (therefore lower average) than multiple smaller water changes adding up to the same volume over the same period of time.

i agree.

 

[jlnguyen74]

In that case, look at vfc's charts. The 50% weekly has nitrate levels from 20-40ppm, while the tank that receives biweekly water changes has nitrate levels from 25-32ppm, all else being equal. Ignore the numbers for a minute, since all tanks are different, but pay attention to the pattern. Wouldn't biweekly be better since you maintain an overall lower nitrate level?

Yes, it would be better. Like I mentioned before, without going through number, and just going by nature observation, more frequent water change at small amount is better than less frequent large water change

 

[vfc]

Let's use a human analogy.

Imagine being confined to a sealed room with a heavy smoker. What would be better for your health:
1- Allowing the smoke to get very dense over a week (to the point of causing you to cough once in a while on the 6th and 7th day) then having 50% of the bad air sucked out and replaced with fresh air.
2-Allowing the air to get stale and every three days 25% of the stale air is sucked out and replaced with fresh air.

Seems like option #1 would be more likely to cross some health threshold and start to cause lung damage over time; which could lead to a shorter life span. Option #2 may just make you feel less energetic and generally sluggish.

 

[jcardona1]

Let's use a human analogy.

Imagine being confined to a sealed room with a heavy smoker. What would be better for your health:
1- Allowing the smoke to get very dense over a week (to the point of causing you to cough once in a while on the 6th and 7th day) then having 50% of the bad air sucked out and replaced with fresh air.
2-Allowing the air to get stale and every three days 25% of the stale air is sucked out and replaced with fresh air.

Seems like option #1 would be more likely to cross some health threshold and start to cause lung damage over time; which could lead to a shorter life span. Option #2 may just make you feel less energetic and generally sluggish.

Or #3, find a bigger room...in other words, don't overstock your tanks

But I agree, I like the sound of #2 for me personally

 

[ScatMan]

In that case, look at vfc's charts. The 50% weekly has nitrate levels from 20-40ppm, while the tank that receives biweekly water changes has nitrate levels from 25-32ppm, all else being equal. Ignore the numbers for a minute, since all tanks are different, but pay attention to the pattern. Wouldn't biweekly be better since you maintain an overall lower nitrate level?

vfc's charts are flawed because he changes the water every 3 days, NOT 3.5 days (aka 50% bi-weekly). the 3 day chart is more than 50% a week hence the appearance of a better option.

25% every 3 days is better than 50% per week given your bio-load parameter (20PPMs/week or ~3PPMs/day). The nitrate swings are less severe.

25% every 3 days does NOT = 50% per week

 

[ScatMan]

Let's use a human analogy.

Imagine being confined to a sealed room with a heavy smoker. What would be better for your health:
1- Allowing the smoke to get very dense over a week (to the point of causing you to cough once in a while on the 6th and 7th day) then having 50% of the bad air sucked out and replaced with fresh air.
2-Allowing the air to get stale and every three days 25% of the stale air is sucked out and replaced with fresh air.

Seems like option #1 would be more likely to cross some health threshold and start to cause lung damage over time; which could lead to a shorter life span. Option #2 may just make you feel less energetic and generally sluggish.

given op's #s you will have the same max nitrate concentration of 40ppm for both 25% bi-weekly and 50% weekly wc.

however, you will have a lower minimum nitrate concentration of 20ppm with the 50% weekly wc, hence a lower average concentration.

 

[ScatMan]

Nothing beats 10% a day. Nothing. Dont discount the best option because is "too much work".

you can't fairly compare 10% a day to 50% per week because at 10% a day you're doing 70% a week, not 50%.

BUT, 70% once a week is better (given op's pollution rate of 20ppm every 7 days) than 10% a day... so 10% a day is NOT "the best option" and is actually more work for less reward.

 

[dxdx]

I don't think anybody pointed out the fact that under scenario number one in the very first post, it starts with minimum nitrate = 30ppm.

The section that reads:

• Minimum nitrate = 30ppm
• Maximum nitrate = 40ppm
• Average nitrate = 35ppm

SHOULD READ

• Minimum nitrate = 20ppm
• Maximum nitrate = 30ppm
• Average nitrate = 25ppm

SO your average nitrate IS actually lower with biweekly water changes. Big fail on that post, unless I'm missing something here....